In the manufacture of semiconductor devices, a substrate such as a semiconductor wafer is subjected to a liquid treatment such as a wet cleaning process, a wet etching process and so on. In a substrate liquid treatment apparatus that performs such liquid treatments, in order to facilitate supplying of a chemical liquid of a stable concentration and a stable temperature to a substrate, there is provided a processing liquid supply unit including a tank that stores a processing liquid, a circulation line connected to the tank, and a plurality of branch lines branched from the circulation line. A processing liquid is supplied to a plurality of processing units through the respective branch lines. The used processing liquid, which has been once supplied to a substrate in each processing unit, is returned to the tank through a recovery line, and is then fed to the circulation line so as to be used again for processing another substrate (see JP2015-220318A, for example).
The used processing liquid having been returned to the tank contains particles. The tank is contaminated if the particles adhere to an inner wall surface of the tank.